AAS 207th Meeting, 8-12 January 2006
Session 62 The COSMOS Survey
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[62.10] A wide angle tail galaxy in the COSMOS field: evidence for cluster formation

V. Smolcic, E. Schinnerer (Max-Planck Institut für Astronomie, Germany), A. Finoguenov (Max-Planck Institut für Extraterrestrische Physik, Germany), I. Sakelliou (Max-Planck Institut für Astronomie, Germany), C. L. Carilli (National Radio Astronomy Observatory, USA), N. Z. Scoville (California Institute of Technology, USA), K. Jahnke (Max-Planck Institut für Astronomie, Germany), VLA-COSMOS Team, COSMOS Collaboration

We have identified a complex galaxy cluster system in the COSMOS deep field via a wide angle tail (WAT) radio galaxy. The WAT galaxy, CWAT-01, is coincident with an elliptical galaxy resolved in the HST-ACS image. Using the COSMOS multiwavelength data set, we derive the radio properties of CWAT-01 and use the optical and X-ray data to investigate its host environment. The cluster hosting CWAT-01 is part of a larger assembly consisting of a minimum of 4 clusters within ~2 Mpc distance identified via diffuse X-ray emission. We apply hydrodynamical models that combine ram pressure and buoyancy forces on CWAT-01. These models explain the shape of the jets only if the galaxy's velocity relative to the intra-cluster medium (ICM) is in the range of about 300-550 km/s. Such a velocity is higher than expected for brightest cluster galaxies (BCGs) if the cluster was a relaxed system. This is an indication that the WAT host cluster is not relaxed, but it is possibly dynamically young. We argue that such a velocity could have been induced through subcluster merger within the CWAT-01 parent cluster and/or cluster-cluster interactions. Our results strongly indicate that we are witnessing the formation of a large cluster from an assembly of multiple clusters, consistent with the hierarchical scenario of structure formation. We estimate the total mass of the final cluster to be approximately 20% of the Coma cluster mass. Finally, our conclusions confirm that WAT galaxies provide an efficient tool for finding galaxy clusters in a dynamically unrelaxed state.

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